In wafer processing, wafers comprising arrays of semiconductor dice are usually received after dicing on a film frame, and are fed to die bonding machines for placement. In a typical die bonding process, dice are detached and lifted from a film frame comprising plastic adhesive film or a Mylar film and are then transferred to a substrate such as a lead frame or printed wiring board (PWB) substrate. Typically, in a pick-up process, a designated die will first be aligned and moved to a location where push-up pins will rise to raise a die from below while the plastic adhesive film is held down by vacuum suction. A collet or pick-up tool is then moved to just above the top surface of the die. The die will be detached from the plastic adhesive film when the push-up pins rise to an appropriate level. The collet provides vacuum suction to hold the die during the action of transferring the die from the plastic adhesive film to the bonding substrate.
Conventionally, for small dice (say, less than 2 mm in width), one ejector pin positioned at the center of the die to be detached is used. However, for larger dice, multiple ejector pins are used in order to evenly distribute the push-up force on the die and reduce a pinching effect by the ejector pins. When the dice get thinner, there is always a chance that a die may break or crack during the detachment process of the die from the plastic adhesive film. The breakage of the die is primarily due to the fact that the stress induced by the pushing up of the pins reaches the critical failure bending stress of the die before the delamination of the interface between the die and the plastic adhesive film takes place. This will be more problematic for (i) dice of bigger size, (ii) thinner dice, and (iii) attachments where there is stronger adhesion force between the die and the plastic adhesive film.
A prior art pick-up process includes a typical push-up mechanism using one ejector pin or multiple ejector pins. FIG. 1 shows a typical layout of the push-up device and its peripheral devices. On a vacuum ejector platform, hole(s) on a cap connected to a vacuum suction supply is used to hold a designated die and the plastic adhesive film in position during the die detachment process. Inside the cap of the vacuum ejector platform, a chuck holds ejector pins and is connected to a motorized mechanism that provides a vertical pushing motion for the ejector pins. During the push-up motion, the ejector pins move upward and push onto a die and the plastic adhesive film. As a result, the die mounted on the plastic adhesive film starts to be delaminated and separates from the film. As the ejector pin rises to certain level, the adhesive force and adhered area between the die and plastic adhesive film are small enough such that it is possible for the pick-up collet to pull the die away from the film by suction means.
U.S. Pat. No. 5,755,373 for a “Die Push-Up Device” uses a die push-up device with only one push-up ejector pin in a bonding machine for semiconductor devices. This invention is applicable for small and thick dice (say, more than 0.2 mm thick). As the size of the die gets bigger (say, more than 5 mm in width), a two-stage ejecting process (such as that in U.S. Pat. No. 4,850,780 for a “Pre-Peel Die Ejector Apparatus”) may be used. In relation to U.S. Pat. No. 5,755,373, using a single ejector pin to perform the die detachment process will not be practical if a thin (less than 0.1 mm thick) and large die (more than 4—mm width) is involved.
For prior art devices using multiple pins, such as U.S. Pat. No. 4,850,780 and US publication number 2001/0017403A1, the locations of the pins are not optimized for handling very thin dice (say, less than 0.1 mm thick). These designs can reduce somewhat the pinching force and minimize any damage to the die during the pick-up process. However, for a large (e.g. more than 4 mm width) and thin (e.g. less than 0.1 mm thick) die, an optimized design for the multiple pushing-up ejector pins is needed in order to prevent the die from cracking during the pick-up process.